IoTServer/src/main/java/cn/minbb/iot/util/LRUCache.java

package cn.minbb.iot.util;

import java.util.HashMap;

// 链表 + HashMap 容器实现
public class LRUCache<K, V> {

    private int cacheCapacity;
    private HashMap<K, CacheNode> caches;
    private CacheNode first;
    private CacheNode last;

    public LRUCache(int size) {
        this.cacheCapacity = size;
        caches = new HashMap<>(size);
    }

    public synchronized void put(K k, V v) {
        CacheNode node = caches.get(k);
        if (node == null) {
            if (caches.size() >= cacheCapacity) {
                caches.remove(last.key);
                removeLast();
            }
            node = new CacheNode();
            node.key = k;
        }
        node.value = v;
        moveToFirst(node);
        caches.put(k, node);
    }

    public synchronized Object get(K k) {
        CacheNode node = caches.get(k);
        if (node == null) {
            return null;
        }
        moveToFirst(node);
        return node.value;
    }

    public synchronized Object remove(K k) {
        CacheNode node = caches.get(k);
        if (node != null) {
            if (node.pre != null) {
                node.pre.next = node.next;
            }
            if (node.next != null) {
                node.next.pre = node.pre;
            }
            if (node == first) {
                first = node.next;
            }
            if (node == last) {
                last = node.pre;
            }
        }
        return caches.remove(k);
    }

    public synchronized void clear() {
        first = null;
        last = null;
        caches.clear();
    }

    private void moveToFirst(CacheNode node) {
        if (first == node) {
            return;
        }
        if (node.next != null) {
            node.next.pre = node.pre;
        }
        if (node.pre != null) {
            node.pre.next = node.next;
        }
        if (node == last) {
            last = last.pre;
        }
        if (first == null || last == null) {
            first = last = node;
            return;
        }
        node.next = first;
        first.pre = node;
        first = node;
        first.pre = null;

    }

    private void removeLast() {
        if (last != null) {
            last = last.pre;
            if (last == null) {
                first = null;
            } else {
                last.next = null;
            }
        }
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        CacheNode node = first;
        while (node != null) {
            sb.append(String.format("%s:%s ", node.key, node.value));
            node = node.next;
        }
        return sb.toString();
    }

    class CacheNode {
        CacheNode pre;
        CacheNode next;
        Object key;
        Object value;

        CacheNode() {
            // 无参构造
        }
    }
}